R loop and append using a row bind

Question

I'm looking for a way to loop through a list of variables that are data and bind them into a single data frame, this will allow me to store the data in the script rather than a separate file. Below is my unsuccessful attemp where I'm now sure what function I need to use to get variable prefixed with "p" to be recognised correctly in the loop.

# Data 

p1 <- c(518458.9470, 6479704.947, 1890.820847)
p2 <- c(518480.0626, 6479701.156, 1890.193591)
p3 <- c(518499.0065, 6479711.374, 1886.774569)

# Create data frame

for (i in 1:3){
  if (i = 1){
    d <- paste0("p",i)
  }else{
    df <- rbind(df, paste("p",i))
  } 
}

Ronak Shah · Accepted Answer · 2021-03-27 01:18:06Z

3

You can use mget to do this without a loop.

data.frame(mget(paste0('p', 1:3)))

#         p1        p2        p3
#1  518458.9  518480.1  518499.0
#2 6479704.9 6479701.2 6479711.4
#3    1890.8    1890.2    1886.8

answered Mar 27, 2021 at 1:18

Ronak Shah

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1 Comment

Markm0705 Over a year ago

I ended up using a transpose to get the data frame shape I wanted... t(data.frame(mget(paste0('p', 1:3))))

tdy · Accepted Answer · 2021-03-26 23:59:29Z

1

In the spirit of your original code, you can get() those variable values by name:

data <- c()
for (i in 1:3) {
    name <- paste0('p', i)
    data <- rbind(data, get(name))
}

A matrix: 3 × 3 of type dbl
518458.9  6479705  1890.821
518480.1  6479701  1890.194
518499.0  6479711  1886.775

answered Mar 26, 2021 at 23:59

tdy

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1 Comment

Markm0705 Over a year ago

I was looking for a data frame as the final output so was easy to change the last line to ... data <- rbind(data, get(name)). Like the way you just used an empty set was used to initialize the variable to be bound to rather than having and if statement

Wiktor Gustafsson · Accepted Answer · 2021-03-26 23:27:10Z

0

Just df <- data.frame(rbind(p1, p2, p3)) should do the job, if I've understood your question correctly.

If those are the only data variables you have, I would skip the middle step of defining the variables and just do

df <- data.frame(
    p1 = c(518458.9470, 6479704.947, 1890.820847),
    p2 = c(518480.0626, 6479701.156, 1890.193591),
    p3 = c(518499.0065, 6479711.374, 1886.774569)
)

It all depends on where your data initially comes from, really.

answered Mar 26, 2021 at 23:27

Wiktor Gustafsson

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4 Comments

Markm0705 Over a year ago

Correct but in practice I have more than three lines of data so loop solution is what I am looking for

Wiktor Gustafsson Over a year ago

Alright, then am I correct in assuming your data is defined in another way than just p1 <- c(...) etc?

Markm0705 Over a year ago

Yes ... the solution above using mget seems the best and avoid the need for a explicit loop

Wiktor Gustafsson Over a year ago

In that case I agree.

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